Quote
DD appeared in my bedroom last night and asked how the entire human race could have appeared from two people. I asked her what she's talking about, Adam and Eve? (turned out she was reading a "Bible Story" book someone gave her, probably step-mom). I told her that it's in the Bible but it wasn't a story that even the author meant for people to take literally. It's questions like this that are driving me crazy. Is that even correct? Did the author of the book of Genesis write it/tell it as a "story" to illustrate a point? Or did the author really intend for people to take it as literal fact? I don't have the knowledge of ancient cultures/history to even have a definitive answer and feel like I can't answer questions like this.

Some people take it literally, which is pretty obviously explained -- they believe the author did mean it literally.

Other people take it symbolically. I've heard that explained a couple ways. Either, it's not as though the people who wrote the bible were sitting there with a notepad and paper, court-reporter style, writing everything word for word -- "Sorry, Moses, could you repeat that? I cannot write down a nod" -- and thus, there are some things that might not be exact. I've also heard it explained that, for example, certain events might have been embellished by the writers to make a better story and thus a better lesson.

Honestly, I'm not sure exactly who believes what and exactly how, but I do know there's no specific consensus -- you don't need to give him a definitive answer.
Also, I would maybe focus on some things too about values, etc that your family believes in just so that he has something definitive to latch onto -- it might help so that he doesn't feel too "lost" while he's figuring everything out.